High efficiency combination direct/indirect water heater

ABSTRACT

A combination direct/indirect liquid heating heater comprises a tower, a cold water inlet conduit causing water to fall in said tower, a hot water reservoir in communication with said tower, a gas burner, a hot gas inlet manifold encased in the reservoir and, by means of a vertical section, directing the gas into the tower. The hot gas manifold vertical section is capped by a cap impeding water flow into the manifold. Also, the vertical section comprises a baffle impeding gas flow from the tower into the reservoir.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of water heaters and, more particularly, the present invention relates to high efficiency devices which heat water using thermal conduction and also via direct contact of the water with combustion gases.

2. Description of the Prior Art

Direct heating of water by combustion gases is known. U.S. Pat. No. 6,089,223 awarded to Jasper et al. on Jul. 18, 2000, and assigned to the instant assignee teaches a heater whereby falling water contacts hot combustion gases.

While direct water heaters are more efficient than indirect-heating configurations, the costs of the former are formidable. For example, the fabrication of housings for the combustion chamber of such units is time consuming, and therefore costly. Also, water switches and additional spray nozzles are necessary to assure adequate cooling of the housings and also of the combustion gases, respectively.

Indirect heating of water by combustion gases occurs when water contacts a heat transfer surface. The heat transfer surface can be defined by one or a plurality of conduits through which hot combustion gas (or some other hot fluid) circulates. Boilers heat water this way.

The heating efficiency of indirect heating systems is low inasmuch as such systems loose heat through the egress of hot combustion gases.

The heating efficiencies of direct systems also can be low in situations where either the combustion gas temperature or the incoming water temperature is too high to facilitate condensation of all the water vapor in the heating zone. Instead, water vapor exits the system, resulting in heat loss. Finally, water-storage tank configurations in typical direct heating systems result in a build-up of vapor pressure above the water level in the tank (i.e., the “head space”) resulting in operating instabilities and further heat losses.

A need exists in the art for an industrial-grade water heater which combines direct with indirect heating functions to maximize heat transfer. The device should enhance the surface area of heat transfer surfaces so as to maximize the time of heat transfer in indirect heating scenarios. The device also should minimize the potential of the development of “hot spots” during operation so as to enhance safety and prolong equipment life.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a high efficiency combination direct/indirect water heater that overcomes many of the disadvantages of the prior art.

It is a further object of the present invention to provide a high efficiency combination direct/indirect water heater that enhances indirect heat transfer. A feature of an embodiment of the present invention is an extended gas-carrying manifold submerged in the water to be heated. In a specific embodiment of the present invention the gas-carrying manifold is encased in a sleeve of water to define a pre-configured annular space. Another feature of the present invention are radially protruding fins from the manifold. An advantage of the present invention is that it ensures that the water to be heated is in constant and close thermal contact with the heated gases during the initial water input mode and in the storage mode, thereby enhancing heat transfer efficiency.

Another object of the present invention is to provide a high efficiency combination direct/indirect water heater that allows unimpeded escape of the heated gases from a heat exchange manifold. A feature of the present invention is that the manifold terminates with a cap structure which prevents water blockage of the heated gas at the egress point. An advantage of the present invention is that the means of egress facilitates unhindered venting of gas and prevents back pressure from occurring at the gas egress point.

Yet another object of the present invention is to provide a high efficiency combination direct/indirect water heater having a water reservoir configuration which prevents combustion gas build-up. A feature of the present invention is the positioning of a combustion gas point of egress adjacent to a water surface point in a vertical riser. An advantage of the present invention is the elimination of any gas head spaces and therefore of the build-up of high gas pressure and the accumulation of high temperature gas between the water level and a solid surface of the heater.

Briefly, the invention provides a water heater comprising: a tower with a cold water inlet conduit causing water to fall through the tower and into a hot water collection tank in communication with the tower; a hot gas manifold adapted to receive hot gases and positioned in the tank so as to be at least partially submerged below the water surface; and a means of gas egress attached to the hot gas manifold and positioned above the water surface, the gas egress means configured to prevent the water falling through the tower from blocking gas egress from the manifold. In an alternative embodiment, the water collection tank surrounding said gas manifold forms an annular space adapted to receive water, the annular space configured to maximize thermal exchange between the manifold and the water residing in the annular space.

BRIEF DESCRIPTION OF THE DRAWING

The foregoing invention and its advantages may be readily appreciated from the following detailed description of the invention, when read in conjunction with the accompanying drawing in which:

FIG. 1 is a cross-sectional view of a combination direct/indirect water heater, in accordance with features of the present invention;

FIG. 2 is a perspective view of a combination direct/indirect water heater, without the tower, in accordance with features of the present invention;

FIG. 3 a is a view of FIG. 1, taken along line 3-3, and shows a cross-sectional view of a heat-transfer manifold included in the water tank of a combination direct/indirect water heater, in accordance with features of the present invention;

FIG. 3 b is a plan view of FIG. 1, taken along line 3-3, of an embodiment of a heat-transfer manifold included in the water tank of a combination direct/indirect water heater, in accordance with features of the present invention;

FIG. 3 c is plan a view of FIG. 1, taken along line 3-3, of another heat-transfer manifold configuration, in accordance with features of the present invention;

FIG. 4 a is a perspective view of a cap over a gas-inlet pipe included in a combination direct/indirect water heater, in accordance with features of the present invention;

FIG. 4 b is a perspective view of an alternative embodiment of a means of egress of combustion gases from a manifold, in accordance with features of the present invention;

FIG. 4 c is a detailed perspective view of a cap over a gas-inlet pipe included in a combination direct/indirect water heater, in accordance with features of the present invention;

FIG. 5 is a cross-sectional view of a specific embodiment of a combination direct/indirect water heater, in accordance with features of the present invention;

FIG. 6 a is a cross-sectional view of FIG. 5, taken along the line 6-6, of a heat-transfer manifold incased in the water tank of a high efficiency combination direct/indirect water heater, in accordance with features of the present invention;

FIG. 6 b is a cross-sectional view of FIG. 5, taken along line 6-6, of an alternative embodiment of a heat-transfer manifold included in the water tank of a high efficiency combination direct/indirect water heater, in accordance with features of the present invention;

FIG. 6 c is a cross-sectional view of FIG. 5, taken along line 6-6, and shows a cross-sectional view of another alternative embodiment of a heat-transfer manifold included in the water tank of a high efficiency combination direct/indirect water heater, in accordance with features of the present invention; and

FIG. 7 is a more complete schematic diagram of the invented heater, in accordance with features of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a high efficiency combination direct/indirect heater that facilitates both direct and indirect heat transfer to a liquid. For the sake of simplicity, it will be assumed throughout this specification that the liquid being heated is water. A salient feature of the invention is the immersion of a heat transfer surface, such as a combustion gas manifold, in already heated water, thereby enhancing efficiencies.

As shown in FIG. 1, the combination direct/indirect water heater, generally designated as numeral 10 is comprised of five main components: a vertical riser 20 (often called “tower”), a cold water supply inlet 30, a hot water reservoir 40, a fuel burner 50, a hot gas inlet conduit or manifold 60 that is nearly fully submerged in the reservoir 40, and a means for water egress 58. FIG. 2 is a perspective view of the invented combination direct/indirect water heater, without the tower.

A water supply and distribution means 30 distributes water 31 so as to contact the water with hot combustion gases 71 emanating from the gas conduit 60. At this juncture, which is approximately midway along the vertically extending space defined by the tower, heat is transferred from the gas to the water in a direct heating mode. To impart additional heat transfer to the incoming water, heat transferring materials 22 are positioned intermediate the water distribution means 30 and the gas egress means 63 of the conduit 60. These transfer materials 22, which typically comprise high surface area, relatively inert materials, are heated continuously by the upwardly traveling gas, thereby imparting heat to the falling water. The transfer materials 22 are supported by a perforated packing shelf 24, (such as a rack) extending transversely to the tower.

The tower 20, the cold water inlet manifold 30, and the gas burner 50 are similar to devices disclosed in U.S. Pat. No. 6,089,223, assigned to the instant assignee, and incorporated herein by reference.

A unique feature of the invented device is that combustion gases produced by the gas burner 50 are released into the partially submerged gas conduit or manifold 60. As depicted in FIG. 1, the manifold is submerged in the collection tank 40 so as to be in direct physical contact with the water previously subjected to direct heating.

Intermediate the gas exit point 63 and the gas means of ingress 61 of the gas manifold 60 is positioned a vertical, upwardly extending conduit section 68. The upwardly extending conduit section 68 terminates with the means of gas egress 63. The means of gas egress is positioned so as to reside in the middle to lower half of the tower 20.

Manifold Configuration Detail

To maximize heat transfer, the submerged combustion gas manifold can effect a circuitous path for the combustion gas to travel, as shown in FIG. 3 a. The manifold depicted in FIG. 3 a comprises a single conduit 64 between ingress point 61 and egress point 62 with a plurality of substantially rectilinear sections 65 serially connected by U-shaped pipe junctions 66.

Alternatively, and as shown in FIG. 3 b, the manifold 60 comprises a plurality of substantially parallel conduits 64 between points 61 and 62. The parallel conduits are intersected at each end by main combustion conduits 53. This design minimizes travel time of combustion gas through the conduit so as to eliminate back pressure to the combustion chamber.

In yet another configuration of the manifold, a spiral design is utilized for the manifold, as depicted in FIG. 3 c.

Optionally, fins substantially radially protruding from the conduits may be added so as to enhance heat transfer from the hot gas to the water in the tank 40. The planar surfaces of these are positioned anywhere between 0° and 90° to the direction of gas flow at the point where the fins are attached to the conduit. For example, as depicted in FIGS. 3 a-3 c, fins 67 are attached so that their plane surfaces are perpendicular to the direction of gas flow. This is particularly advantageous for maximizing heat transfer to the water. Also depicted in FIG. 3 a are fins 59 directed along the direction of gas flow.

A variety of materials are suitable for fabrication of the gas manifold 60, as long as the material is impermeable to the liquid being heated, and tolerant to the gas temperatures emanating from the combustion chamber.

Preventing Water from Entering The Gas Manifold.

To prevent water from entering the means of gas egress, the combustion gas manifold terminates in a cap 70 positioned distal to the rim 69 of the vertical conduit 68, thereby defining the means of gas egress 63. Specific embodiments of the means of gas egress are depicted in FIGS. 4 a, 4 b, and 4 c. In practice, other embodiments may be employed by combining features of two or three of the depicted embodiments. The cap 70 is so positioned as to allow streams 71 of the hot gas to circumvent it and to contact the downward falling water 31. As shown in FIG. 4 a, a plurality of circumferentially spaced apertures 80 about the rim 69 can be provided so as to allow venting of the gas from the means of egress and inferior to the position of the cap 70. Several methods can be used to support the cap. In FIG. 4 a the cap is mounted at some distance above the point of gas egress 63 by means of a plurality of supporting rods 73 attached to a ring 51 encircling the rim 69 of the gas conduit 68. In FIG. 4 b the cap 70 is attached to the riser by means of a perforated plate 21, but brackets or other means of support can be employed. FIG. 4 c depicts an alternative embodiment wherein the cap is attached to the gas conduit 68 by means of four plates 89 and wherein circumferentially spaced apertures 80 on a vertical portion 74 of the cap 70 are provided so as to allow venting of the gas.

To prevent a laminar flow of water from fanning out from the top 81 of the cap 70, (which would lead to the impedance of gas from the means of egress), the cap 70 is so contoured as to prevent formation of such laminar water flow. As shown in FIGS. 2, 4 a, and 4 c, the cap 70 comprises a vertical cylindrical portion 74, to which is attached a radially protruding conical brim or a series of conical flaps 75. Formation of laminar water flow around such an irregularly shaped cap is substantially prevented by the conical brim 75 or flaps. As shown in FIGS. 2 and 4 a, the conical flaps also provide protection from water entry into the gas egress apertures 80. A variety of other cap embodiments comprising irregular surfaces achieve the same anti-laminar-flow objective. FIG. 4 b depicts a cap with an hemispherical top 93 the inside surface 91 of which allows a smoother redirection of the combustion gas 71. Optionally, as shown in FIG. 4 c, flaps 85 mounted above the apertures 80 prevent water from entering into the gas conduit.

Also shown in FIG. 4 b is a cooling ring 56 positioned in the annular space 32 defined by the inwardly facing surface 82 of the riser and the outwardly facing surface of the conduit 68. As depicted in FIG. 4 b this cooling ring 56 is a plate separated from the conduit 68 and the riser 40 by narrow gaps arranged along its inner and outer peripheries. The cooling ring is skip welded to the inward pointing surface 82 of the riser 40 at locations 57. The cooling ring 56 allows water to collect at this point, but one or more overflow ports 54 ensure that the water does not reach the gas egress point 63. The cooling ring facilitates impact of the falling water with the outwardly facing surface of the conduit 60 and the inwardly facing surface 82 of the riser.

Preventing Gas from Entering The Water Reservoir.

After cascading downwardly past the cap 70, the falling water enters the collection and storage tank 40 where it forms a volume of hot water 41 having a water surface 42. In as much as the cap 70 covering the gas inlet conduit 68 inevitably directs downward some of the hot gas to the water surface 42, a provision is made to prevent the hot gas from becoming trapped in the head space 43 defined by an inside top surface 45 of the storage tank which opposes the water surface 42.

To prevent gas from being trapped in the head space 43, a baffle 77 is provided to deflect downwardly-flowing gas away from the water surface 42 and head space 43. As depicted in FIG. 4 a, the baffle comprises a substrate radially extending from the upwardly extending conduit section 68. Typically, the baffle is positioned coaxial with the conduit 68 with the plane of the baffle parallel to and above the top of the collection tank 40. The periphery of the baffle 77 opposes an interior surface 79 of the upwardly extending tower 20 so as to define an annular passageway 78 through which water cascades. The width of the passageway is dimensioned so as not to impede downward water passage while also preventing substantial gas volumes from passing downwardly through the passageway. Generally, the diameter of the baffle 77 is greater than the diameter of the cap 70.

In the embodiment depicted in FIG. 4 b, the cooling ring 56 serves the same function as the baffle 77 in FIG. 4 a.

A Sleeve-Shaped Reservoir

A feature of a specific embodiment of the invented device is depicted in FIG. 5. In this embodiment the hot gases produced by the gas burner 50 are released into a gas conduit or manifold 160 which is substantially submerged in a reservoir 140.

To maximize heat transfer, a longitudinally extending exterior surface of the heated-gas manifold 160 is juxtaposed in spacial relation to interior surfaces 164 of the reservoir 140. More specifically, an inwardly-facing surface 164 of the reservoir serves as a sleeve encasing the manifold and spaced from the manifold so as to maximize the ratio of manifold surface area to water volume as shown in FIG. 5.

In cases where the cross section of the manifold and the cross section of the sleeve are both circular, an annular space 163 is defined by an inside surface 164 of the reservoir opposing a longitudinally extending exterior surface 165 of the manifold 160. The distance Δ between the opposing surfaces is generally maintained to ensure maximum heat exchange from the manifold. In one embodiment, in order to minimize turbulence in the water flow, the distance Δ is kept constant, no matter what circuitous route the conduit takes.

To further maximize heat transfer, the diameter of the manifold is typically 30 to 60% of the diameter of the enveloping sleeve and preferably 40 to 56% the diameter of the enveloping sleeve.

FIGS. 6 a-6 c are cross-sectional views of FIG. 5, taken along the line 6-6. The manifold depicted in cross-section in FIG. 6 a comprises a single cylindrical conduit 160 nested inside a sleeve 140. The surface of the conduit defines a smooth uninterrupted surface to facilitate rapid laminar flow of water along the surface.

The manifold depicted in cross-section in FIG. 6 b comprises a single conduit 160 with, optionally, a plurality of substantially radial protruding sections or fins welded or otherwise suitably thermally connected to the manifold 160. These fins may be aligned along the direction of gas flow (fins 166) or orthogonal thereto (fins 167) or at any angle there-between. The fins enhance heat transfer from the hot gas to the water in the tank 140. The radially protruding sections are utilized in situations where calcification build-up is not an issue. FIG. 6 c depicts a detail of an alternative embodiment wherein the hot gas manifold 160 has a corrugated cross-section. This corrugated manifold can also be used in conjunction with the embodiment depicted in FIGS. 1-3 c.

FIG. 7 provides a more complete schematic diagram of the invented device. Specifically, FIG. 7 shows a high temperature shut down sensor 120 and high water sensors 130 located below the gas egress point 63. The “high water” sensors allow shut off of the device when water threatens to flood the gas conduit 60. The “low water” sensors 150 allow shut off of the device when it threatens to overheat. Also provided is a heater overflow pipe 140. Also depicted are components of the device discussed supra: the fuel burner 50, the firing chamber 60, the water storage tank 40, the cooling ring 56, the protective cap 70, the heat transfer rings 22, and the inlet nozzles 31.

The foregoing description is for purposes of illustration only and is not intended to limit the scope of protection accorded this invention. The present invention may be presented in other specific embodiments without departing from the essential attributes of the present invention. It is apparent that many modifications, substitutions, and additions may be made to the preferred embodiment while remaining within the scope of the appended claims, which should be interpreted as broadly as possible. 

1. A combination direct/indirect liquid heating device comprising a tower; a cold water inlet conduit in communication with a first end of said tower; a hot water collection tank in communication with said tower, said tank adapted to collect water and there form a water surface; a hot gas manifold having a first end adapted to receive hot gases, said manifold positioned in the tank so as to be partially submerged below the water surface; and a means of gas egress attached to a second end of said manifold and positioned above the water surface, the egress means configured to prevent water from entering said manifold. 2 The device as recited in claim 1 wherein said manifold comprises sections providing parallel paths for the gas.
 3. The device as recited in claim 1 wherein said manifold comprises sections providing a continuous path for the gas.
 4. The device as recited in claim 1 wherein exterior regions of said manifold comprise protruding fins.
 5. The device as recited in claim 1 wherein a second end of said manifold terminates with a vertical section extending upwardly into the tower.
 6. The device as recited in claim 5 wherein said vertical section comprises a baffle impeding gas flow from the tower into the collection tank.
 7. The device as recited in claim 5 wherein said vertical section is terminated by the means of gas egress.
 8. The device as recited in claim 1 wherein said means of gas egress comprises a cap configured to impede formation of laminar water flow around the periphery of said cap.
 9. The device as recited in claim 8 wherein said means comprises a flat region, a conical peripheral region and a vertical cylindrical region.
 10. The device as recited in claim 8 wherein said conical peripheral region is pleated.
 11. The device as recited in claim 1 wherein said water collection tank comprises a sleeve surrounding said gas conduit so as to form an annular space adapted to receive water.
 12. The device as recited in claim 8 wherein said cap comprises a hemispherical region.
 13. The device as recited in claim 1 further comprising a cooling ring positioned on said gas manifold at a point proximal to the means of gas egress, said cooling ring comprising a plate with one or more overflow ports and with gaps arranged along inner and outer peripheries of the plate so as to direct the fall of water.
 14. The device as recited in claim 11 wherein said manifold is corrugated.
 15. A water heater comprising: a longitudinally extending gas conduit terminating in a means of gas egress; a sleeve surrounding said gas conduit so as to form an annular space adapted to receive water; a means for contacting water with gas emanating from the gas egress means; a means for water ingress to the annular space; and a means for water egress from the annular space.
 16. The heater as recited in claim 15 wherein a vertical riser is integrally molded to said sleeve.
 17. The heater as recited in claim 15 wherein said conduit terminates with a vertical section extending upwardly into a tower.
 18. The heater as recited in claim 15 wherein the distance between the conduit and the sleeve remains constant along a longitudinally-extending region of the conduit.
 19. The heater as recited in claim 15 further comprising a heater overflow pipe and means to maintain the water temperature and volume within predetermined levels. 